Imaging compositions disclosed in commonly-owned U.S. application Ser. No. 971,460, filed on Dec. 20, 1978, entitled "Inhibition of Image Formation Utilizing Cobalt(III) Complexes", as well as in Research Disclosure, Vol. 184, Publication No. 18436, dated August, 1979, published by Industrial Opportunities, Ltd., Homewell, Havant, Hampshire, PO9 1EF, United Kingdom, comprise an image precursor composition that includes cobalt(III) complexes containing releasable ligands. The image precursor composition is light-activatible through the use of a photoactivator, or it is heat-activatible, optionally through the use of a thermal destabilizer. A wide variety of such thermal destabilizers are disclosed.
Such image precursor compositions that rely upon a thermal destabilizer have, prior to this invention, necessitated heating the exposed imaging element to substantial temperatures, e.g., temperatures equal to or greater than 125.degree. C. The initiation of the thermal destabilizing reaction required such high temperatures. Examples of such thermal destabilizers and their initiation temperatures (stated as a heating temperature for initial dye development) are described in said U.S. Ser. No. 971,460.
In some instances, such temperatures cause some undesirable dimensional changes in the imaging element. Therefore, prior to this invention, a need existed for a thermal destabilizer composition having an initiation temperature significantly below 125.degree. C. Although a few of the destabilizers of the aforesaid application, such as o-hydroxyphenyl urea, may have such lowered initiation temperatures when used individually in a fresh composition, they do not after being stored (incubated) at 38.degree. C. and 50% relative humidity for two weeks following their conversion into a coating. A composition, usually in the form of a coating, having an initiation temperature below 125.degree. C. only when used fresh is not as practical as one that has such an initiation temperature even after storage.